New Zealand’s Approach to Ecological Risk Assessments for Marine Mammals

To underpin the assessment and management of the effects of fishing and other threats on marine mammals, New Zealand has developed a quantitative, spatially-explicit, seasonally-disaggregated risk assessment framework to estimate the likelihood and degree to which human-induced mortalities may exceed population impact reference levels. The method uses the spatial overlap of threat effort and species distribution; observed or estimated mortality rates; and population-specific estimates of abundance and productivity. It generates estimates of total mortalities that can be compared with explicit or implied management targets or limits (e.g. Potential Biological Removal) to estimate the risk of not achieving those objectives. The method generates absolute rather than relative estimates of impact and risk, propagates uncertainty in all inputs, and provides for disaggregation of risk at a variety of spatial and temporal scales. Such risk assessments therefore provide a powerful tool for scientists and resource managers to target and prioritize information collection, mitigation, or management action. A variant of this method has been successfully applied to assess the risk posed by multiple threats to a single taxon (Maui’s dolphin), and another variant is currently being applied to assess the risk posed by commercial fisheries across all marine mammal taxa resident in New Zealand.